This application is a continuation-in-part of application Ser. No. 09/212,926, entitled xe2x80x9cMethod of Making Light Emitting Polymer Composite Materialxe2x80x9d filed Dec. 16, 1998, now U.S. Pat. No. 6,228,436.
The present invention relates generally to a method of making composite polymer films. More specifically, the present invention relates to making a composite polymer film from a mixture having molecular dopant in a liquid polymer precursor. Additional charge transport layers, or layers of polymer or metal may be added under vacuum as well.
As used herein, the term xe2x80x9cpolymer precursorxe2x80x9d includes monomers, oligomers, and resins, and combinations thereof. As used herein, the term xe2x80x9cmonomerxe2x80x9d is defined as a molecule of simple structure and low molecular weight that is capable of combining with a number of like or unlike molecules to form a polymer. Examples include, but are not limited to, simple acrylate molecules, for example, hexanedioldiacrylate, and tetraethyleneglycoldiacrylate, styrene, methyl styrene, and combinations thereof. The molecular weight of monomers is generally less than 1000, while for fluorinated monomers, it is generally less than 2000. Substructures such as CH3, t-butyl, and CN can also be included. Monomers may be combined to form oligomers and resins, but do not combine to form other monomers.
As used herein, the term xe2x80x9coligomerxe2x80x9d is defined as a compound molecule of at least two monomers that can be cured by radiation, such as ultraviolet, electron beam, or x-ray, glow discharge ionization, and spontaneous thermally induced curing. Oligomers include low molecular weight resins. Low molecular weight is defined herein as about 1000 to about 20,000 exclusive of fluorinated monomers. Oligomers are usually liquid or easily liquifiable. Oligomers do not combine to form monomers.
As used herein, the term xe2x80x9cresinxe2x80x9d is defined as a compound having a higher molecular weight (generally greater than 20,000) which is generally solid with no definite melting point. Examples include, but are not limited to, polystyrene resins, epoxy polyamine resins, phenolic resins, acrylic resins (for example, polymethylmethacrylate), and combinations thereof.
As used herein, the term xe2x80x9cparticlexe2x80x9d is defined as a minute piece of matter, which can be as small as an atom or molecule or have a size up to ten micrometers.
As used herein, the term xe2x80x9c(meth)acrylatexe2x80x9d includes both acrylates and methacrylates, and xe2x80x9c(meth)acrylicxe2x80x9d includes both acrylic and methacrylic.
As used herein, the term xe2x80x9ccomposite polymerxe2x80x9d is defined as a polymer having one or more phases. If it has two phases, a first phase is substantially continuous and encompasses xe2x80x9cislandsxe2x80x9d of a second phase from the molecular level to molecular aggregate level. The xe2x80x9cislandsxe2x80x9d of the second phase may touch and/or the two phases may be unlinked or linked, but they do not provide a continuous conjugated network. As used herein, the term xe2x80x9cconjugatedxe2x80x9d refers to a chemical structure of alternating single and double bonds between carbon atoms in a carbon atom chain. The composite polymer will have only one phase if the molecular dopant is soluble in the polymer precursor.
As used herein, the term xe2x80x9ccryocondensexe2x80x9d and forms thereof refer to the physical phenomenon of a phase change from a gas phase to a liquid phase upon the gas contacting a surface having a temperature lower than a dew point of the gas.
The basic process of plasma enhanced chemical vapor deposition (PECVD) is described in THIN FILM PROCESSES, J. L. Vossen, W. Kern, editors, Academic Press, 1978, Part IV, Chapter IV-1 Plasma Deposition of Inorganic Compounds, Chapter IV-2 Glow Discharge Polymerization, which is incorporated herein by reference. Briefly, a glow discharge plasma is generated on an electrode that may be smooth or have pointed projections. Traditionally, a gas inlet introduces high vapor pressure monomeric gases into the plasma region wherein radicals are formed so that upon subsequent collisions with the substrate, some of the radicals in the monomers chemically bond or cross link (cure) on the substrate. The high vapor pressure monomeric gases include gases of CH4, SiH4, C2H6, C2H2, or gases generated from high vapor pressure liquid, for example styrene (10 torr at 87.4xc2x0 F. (30.8xc2x0 C.)), hexane (100 torr at 60.4xc2x0 F. (15.8xc2x0 C.)), tetramethyldisiloxane (10 torr at 82.9xc2x0 F. (28.3xc2x0 C.)) and 1,3,-dichlorotetra-methyldisiloxane (75 torr at 44.6xc2x0 F. (7.0xc2x0 C.)), and combinations thereof, that may be evaporated with mild controlled heating. Because these high vapor pressure monomeric gases do not readily cryocondense at ambient or elevated temperatures, deposition rates are low (a few tenths of micrometer/min maximum) relying on radicals chemically bonding to the surface of interest instead of cryocondensation. Remission due to etching of the surface of interest by the plasma competes with reactive deposition. Lower vapor pressure species have not been used in PECVD because heating the higher molecular weight monomers to a temperature sufficient to vaporize them generally causes a reaction prior to vaporization, or metering of the gas becomes difficult to control, either of which is inoperative.
The basic process of flash evaporation is described in U.S. Pat. No. 4,954,371, which is incorporated herein by reference. This basic process may also be referred to as polymer multi-layer (PML) flash evaporation. Briefly, a radiation polymerizable and/or cross linkable material is supplied at a temperature below a decomposition temperature and polymerization temperature of the material. The material is atomized to droplets having a droplet size ranging from about 1 to about 50 microns. An ultrasonic atomizer is generally used. The droplets are then flash vaporized, under vacuum, by contact with a heated surface above the boiling point of the material, but below the temperature which would cause pyrolysis. The vapor is cryocondensed on a substrate, then radiation polymerized or cross linked as a very thin polymer layer.
According to the state of the art of making plasma polymerized films, PECVD and flash evaporation or glow discharge plasma deposition and flash evaporation have not been used in combination. However, plasma treatment of a substrate using a glow discharge plasma generator with inorganic compounds has been used in combination with flash evaporation under a low pressure (vacuum) atmosphere as reported in J. D. Affinito, M. E. Gross, C. A. Coronado, and P. M. Martin, xe2x80x9cVacuum Deposition Of Polymer Electrolytes On Flexible Substrates,xe2x80x9d Proceedings of the Ninth International Conference on Vacuum Web Coating, November 1995, ed. R. Bakish, Bakish Press 1995, pg. 20-36, and as shown in FIG. 1a. In that system, the plasma generator 100 is used to etch the surface 102 of a moving substrate 104 in preparation to receive the monomeric gaseous output from the flash evaporation 106 that cryocondenses on the etched surface 102 and is then passed by a first curing station (not shown), for example, electron beam or ultraviolet radiation, to initiate cross linking and curing. The plasma generator 100 has a housing 108 with a gas inlet 110. The gas may be oxygen, nitrogen, water or an inert gas, for example argon, or combinations thereof. Internally, an electrode 112 that is smooth or having one or more pointed projections 114 produces a glow discharge and makes a plasma with the gas which etches the surface 102. The flash evaporator 106 has a housing 116, with a monomer inlet 118 and an atomizing nozzle 120, for example an ultrasonic atomizer. Flow through the nozzle 120 is atomized into particles or droplets 122 which strike the heated surface 124 whereupon the particles or droplets 122 are flash evaporated into a gas that flows past a series of baffles 126 (optional) to an outlet 128 and cryocondenses on the surface 102. Although other gas flow distribution arrangements have been used, it has been found that the baffles 126 provide adequate gas flow distribution or uniformity while permitting ease of scaling up to large surfaces 102. A curing station (not shown) is located downstream of the flash evaporator 106. The monomer may be a (meth)acrylate (FIG. 1b).
Organic light emitting polymers may be long chain conjugated polymers with molecular weights on the order of 1 dalton, or small molecules, for example, metal (8-quinolinolato) chelates, quinacridone derivatives, or triaryl amine derivatives. Fabrication of organic light emitting devices (OLED) with small molecules has been with (1) conventional electron beam or thermal evaporation or sublimation of a solid small molecule material from a crucible; (2) spin coating of the small molecule material suspended in a solution of solvent and a polymeric binder followed by removal of the solvent; and (3) spin coating as for (2) but with a polymeric electrolyte binder. The evaporation/sublimation methods produce a film that is substantially composed of the light emitting small molecule. These methods offer high deposition rates, and other advantages, but suffer from the disadvantage of the difficulty of evaporating the small molecule material without significant thermal degradation. In spin coating, the film produced is a composite of a molecularly doped polymer (MDP) wherein the small molecules are dispersed throughout either a polymer or electrolyte. However, it is difficult to control thickness within the few hundred angstrom range necessary to control turn-on voltage.
Therefore, there is a need for an improved method of making molecularly doped polymer (MDP).
The present invention satisfies this need by providing a method of making a composite polymer of a molecularly doped polymer. The method includes mixing a liquid polymer precursor with molecular dopant forming a molecularly doped polymer precursor mixture, flash evaporating the molecularly doped polymer precursor mixture forming a composite vapor, and cryocondensing the composite vapor on a cool substrate forming a cryocondensed composite molecularly doped polymer precursor layer and cross linking the cryocondensed composite molecularly doped polymer precursor layer thereby forming a layer of the composite polymer of the molecularly doped polymer.
The flash evaporating may be performed by supplying a continuous liquid flow of the molecularly doped polymer precursor mixture into a vacuum environment at a temperature below both the decomposition temperature and the polymerization temperature of the molecularly doped polymer precursor mixture, continuously atomizing the molecularly doped polymer precursor mixture into a continuous flow of droplets, and continuously vaporizing the droplets by continuously contacting the droplets on a heated surface having a temperature at or above a boiling point of the liquid polymer precursor and of the molecular dopant, but below a pyrolysis temperature, forming the composite vapor. The droplets typically range in size from about 1 micrometer to about 50 micrometers, but they could be smaller or larger.
Alternatively, the flash evaporating may be performed by supplying a continuous liquid flow of the molecularly doped polymer precursor mixture into a vacuum environment at a temperature below both the decomposition temperature and the polymerization temperature of the molecularly doped polymer precursor mixture, and continuously directly vaporizing the liquid flow of the molecularly doped polymer precursor mixture by continuously contacting the molecularly doped polymer precursor mixture on a heated surface having a temperature at or above a boiling point of the liquid polymer precursor and of the molecular dopant, but below a pyrolysis temperature, forming the composite vapor.
The molecular dopant may be soluble in the polymer precursor, insoluble in the polymer precursor, and partially soluble in the polymer precursor, and combinations thereof. If the dopant material is a liquid, it may be any type having a boiling point below the temperature of the heated surface in the flash evaporation process. Molecular dopants include, but are not limited to, organic solids, organic liquids, and combinations thereof. Organic solids include, but are not limited to, metal (8-quinolinolato) chelates, phenyl acetylene, triaryl amine derivatives, quinacridone derivatives, and combinations thereof. Organic liquids include, but are not limited to, substituted metal tris(N-R 8-quinolinolato) chelates, and substituted tertiary aromatic amines, and combinations thereof:
The molecular dopant may be sufficiently small with respect to particle density and liquid polymer precursor density and viscosity that the settling rate of the molecular dopant within the liquid polymer precursor is several times greater than the amount of time to transport a portion of the liquid molecularly doped polymer precursor mixture from a reservoir to the atomization nozzle. The molecular dopant may vary in size from a single molecule or atom to about 1 xcexcm maximum. The maximum size should generally be less than the thickness of the particle layer in an OLED, i.e., about 1000 Angstroms.
The polymer precursors may be monomers, oligomers, and resins, and combinations thereof. Examples of monomers include, but are not limited to, (meth)acrylate molecules, for example, hexanedioldiacrylate, and tetraethyleneglycoldiacrylate, styrene, and methyl styrene, and combinations thereof. Oligomers, include, but are not limited to, polyethylene glycol diacrylate 200, polyethylene glycol diacrylate 400, and polyethylene glycol diacrylate 600, tripropyleneglycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol monoacrylate, and caprolactone acrylate, and combinations thereof. Resins include, but are not limited to, polystyrene resins, epoxy polyamine resins, phenolic resins, and (meth)acrylic resins, and combinations thereof.
The cross linking may be by radiation, including ultraviolet, electron beam, and x-ray, glow discharge ionization, and spontaneous thermal induced cross linking.
Organic optoelectronic devices can be made using crosslinked molecularly doped polymer layers. Organic optoelectronic devices include, but are not limited to, organic light emitting devices, liquid crystal displays, photo diodes, light modulators for telecommunications, wave guides, solar cells, and integrated optics. The organic optoelectronic device may include a first electrode, a hole transport layer, an active layer, an electron transport layer, and a second electrode. One or more of the hole transport layer, the active layer, and the electron transport layer, may be crosslinked molecularly doped polymer layers. The organic optoelectronic device optionally includes a charge injection layer, and a hole blocking layer. The first electrode may be a transparent conductive oxide, and the second electrode may be a metal cathode. Active layers include, but are not limited to, light emitting layers, light absorbing layers, and electric current generating layers.
When the hole transport layer is the molecularly doped polymer layer, the molecular dopant includes, but is not limited to, tertiary aromatic amines. When the active layer is the molecularly doped polymer layer, the molecular dopant includes, but is not limited to, metal (8-quinolinolato) chelates, quinacridone derivatives, and triaryl amine derivatives. When the electron transport layer is the molecularly doped polymer layer, the molecular dopant includes, but is not limited to, metal (8-quinolinolato) chelates.
Another aspect of the invention involves a method of making an organic optoelectronic device. The method includes depositing a first electrode adjacent a substrate, depositing a hole transport layer adjacent the first electrode, depositing an active layer adjacent the hole transport layer, depositing an electron transport layer adjacent the active layer, and depositing a second electrode adjacent the electron transport layer, wherein at least one of the layers selected from the group consisting of the hole transport layer, the active layer, and the electron transport layer, and combinations thereof, comprises a crosslinked molecularly doped polymer layer. Optionally, a charge injection layer can be deposited adjacent to the first electrode before the hole injection layer is deposited, and/or a hole blocking layer can be deposited adjacent to the electron transport layer before the second electrode is deposited. By adjacent, we mean next to, but not necessarily directly next to. There can be additional layers intervening between the adjacent layers.
The molecularly doped polymer layer can be made by mixing a liquid polymer precursor with molecular dopant forming a molecularly doped polymer precursor mixture, flash evaporating the molecularly doped polymer precursor mixture forming a composite vapor, and cryocondensing the composite vapor on a cool substrate forming a cryocondensed composite molecularly doped polymer precursor layer and cross linking the cryocondensed composite molecularly doped polymer precursor layer thereby forming a layer of the composite polymer of the molecularly doped polymer.
Accordingly, it is an object of the present invention to provide a method of making a composite polymer of a molecularly doped polymer.